Acyclic dialkyl complex

Seebach and Daum (75) investigated the properties of a chiral acyclic diol, 1,4-bis(dimethylamino)-(2S,35)- and (2K,3/ )-butane-2,3-diol (52) as a chiral auxiliary reagent for complexing with LAH. The diol is readily available from diethyl tartrate by conversion to the dimethylamide and reduction with LAH. The diol 52 could be converted to a 1 1 complex (53) with LAH (eq. [18]), which was used for the reduction of aldehydes and ketones in optical yields up to 75%. Since both enantiomers of 53 are available, dextro- or levorotatory products may be prepared. The chiral diol is readily recoverable without loss of optical activity. The (- )-52-LAH complex reduced dialkyl and aryl alkyl ketones to products enriched in the (S)-carbinol, whereas (+ )-52-LAH gives the opposite result. The highest optical yield of 75% was obtained in the reduction of 2,4,6-... 

Besides being aq clic, another confounding factor with this substrate is that it is secondary, so the product still contains an active proton such that racemiza-tion and dialkylation are concerns. However, neither of these potential obstacles were problems in this chemistry since the monoalkylated product is 4 pKa units less acidic than the starting active methylene compound [23]. A further complication of the acyclic enolate is that both Z- and -enolates can be formed, and these are likely to complex differently with the catalyst. A computational study suggested that the Z-enolate complexes to the cinchoninium catalyst more strongly than the -enolate, and this enolate fits into a groove of the catalyst rather than directly in a face-to-face orientation. However, calculations could not determine any trends or patterns to explain the enantioselectivity [18]. 

Besides these alkylations of soft nucleophiles with cr-alkenylpalladium intermediates, 7T-allylpalladium complexes, formed by carbopalladation of an allene with an arylpalla-dium halide intermediate, are able to cyclize by attacking a dialkyl malonate moiety (Scheme 20)P° Instead of allenes, which give methyleneindane derivatives, cyclic and acyclic 1,4-dienes have been employed to yield tetrahydronaphthalene derivatives in good yieldsl ... 

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